Excessive menstrual bleeding plus clear water discharge? ?

My last two periods have started off very strange. My period usually will start by releasing this clear odorless watery liquid that will soak through my tampon. Ill have to change my tampon every few hours because it gets filled with water. Then after this happends, usually on the third day, my peiod will begin. Ive always had very painfull periods and heavy bleeding, but this time I experienced extreme heavy bleeding. I ped several blood clots the size of circle using your thumb and index finger. I would change my tampon every 20 minutes at one point. After three days of this bleeding, the watery discharge was back and the period had stopped. I am confused. Does anyone know what could be causing the water to come out?